[PATCH v3 27/29] arm_mpam: Add helper to reset saved mbwu state

[James Morse <james.morse@arm.com>]

resctrl expects to reset the bandwidth counters when the filesystem
is mounted.

To allow this, add a helper that clears the saved mbwu state. Instead
of cross calling to each CPU that can access the component MSC to
write to the counter, set a flag that causes it to be zero'd on the
the next read. This is easily done by forcing a configuration update.

Signed-off-by: James Morse <james.morse@arm.com>
Reviewed-by: Fenghua Yu <fenghuay@nvdia.com>
Tested-by: Fenghua Yu <fenghuay@nvidia.com>
---
Changes since v2:
 * Switched to guard and fixed non _srcu list walker.
 * Made a comment about what is proteted by which lock a list.
---
 drivers/resctrl/mpam_devices.c  | 46 ++++++++++++++++++++++++++++++++-
 drivers/resctrl/mpam_internal.h |  7 ++++-
 2 files changed, 51 insertions(+), 2 deletions(-)

diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
index c207a6d2832c..89d4f42168ed 100644
--- a/drivers/resctrl/mpam_devices.c
+++ b/drivers/resctrl/mpam_devices.c
@@ -1066,9 +1066,11 @@ static u64 mpam_msmon_overflow_val(enum mpam_device_features type)
 static void __ris_msmon_read(void *arg)
 {
 	bool nrdy = false;
+	bool config_mismatch;
 	struct mon_read *m = arg;
 	u64 now, overflow_val = 0;
 	struct mon_cfg *ctx = m->ctx;
+	bool reset_on_next_read = false;
 	struct mpam_msc_ris *ris = m->ris;
 	struct msmon_mbwu_state *mbwu_state;
 	struct mpam_props *rprops = &ris->props;
@@ -1083,6 +1085,14 @@ static void __ris_msmon_read(void *arg)
 		  FIELD_PREP(MSMON_CFG_MON_SEL_RIS, ris->ris_idx);
 	mpam_write_monsel_reg(msc, CFG_MON_SEL, mon_sel);
 
+	if (m->type == mpam_feat_msmon_mbwu) {
+		mbwu_state = &ris->mbwu_state[ctx->mon];
+		if (mbwu_state) {
+			reset_on_next_read = mbwu_state->reset_on_next_read;
+			mbwu_state->reset_on_next_read = false;
+		}
+	}
+
 	/*
 	 * Read the existing configuration to avoid re-writing the same values.
 	 * This saves waiting for 'nrdy' on subsequent reads.
@@ -1090,7 +1100,10 @@ static void __ris_msmon_read(void *arg)
 	read_msmon_ctl_flt_vals(m, &cur_ctl, &cur_flt);
 	clean_msmon_ctl_val(&cur_ctl);
 	gen_msmon_ctl_flt_vals(m, &ctl_val, &flt_val);
-	if (cur_flt != flt_val || cur_ctl != (ctl_val | MSMON_CFG_x_CTL_EN))
+	config_mismatch = cur_flt != flt_val ||
+			  cur_ctl != (ctl_val | MSMON_CFG_x_CTL_EN);
+
+	if (config_mismatch || reset_on_next_read)
 		write_msmon_ctl_flt_vals(m, ctl_val, flt_val);
 
 	switch (m->type) {
@@ -1242,6 +1255,37 @@ int mpam_msmon_read(struct mpam_component *comp, struct mon_cfg *ctx,
 	return err;
 }
 
+void mpam_msmon_reset_mbwu(struct mpam_component *comp, struct mon_cfg *ctx)
+{
+	struct mpam_msc *msc;
+	struct mpam_vmsc *vmsc;
+	struct mpam_msc_ris *ris;
+
+	if (!mpam_is_enabled())
+		return;
+
+	guard(srcu)(&mpam_srcu);
+	list_for_each_entry_srcu(vmsc, &comp->vmsc, comp_list,
+				 srcu_read_lock_held(&mpam_srcu)) {
+		if (!mpam_has_feature(mpam_feat_msmon_mbwu, &vmsc->props))
+			continue;
+
+		msc = vmsc->msc;
+		list_for_each_entry_srcu(ris, &vmsc->ris, vmsc_list,
+					 srcu_read_lock_held(&mpam_srcu)) {
+			if (!mpam_has_feature(mpam_feat_msmon_mbwu, &ris->props))
+				continue;
+
+			if (WARN_ON_ONCE(!mpam_mon_sel_lock(msc)))
+				continue;
+
+			ris->mbwu_state[ctx->mon].correction = 0;
+			ris->mbwu_state[ctx->mon].reset_on_next_read = true;
+			mpam_mon_sel_unlock(msc);
+		}
+	}
+}
+
 static void mpam_reset_msc_bitmap(struct mpam_msc *msc, u16 reg, u16 wd)
 {
 	u32 num_words, msb;
diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
index ff38b4bbfc2b..6632699ae814 100644
--- a/drivers/resctrl/mpam_internal.h
+++ b/drivers/resctrl/mpam_internal.h
@@ -204,10 +204,14 @@ struct mon_cfg {
 
 /*
  * Changes to enabled and cfg are protected by the msc->lock.
- * Changes to prev_val and correction are protected by the msc's mon_sel_lock.
+ * The msc's mon_sel_lock protects:
+ * - reset_on_next_read
+ * - prev_val
+ * - correction
  */
 struct msmon_mbwu_state {
 	bool		enabled;
+	bool		reset_on_next_read;
 	struct mon_cfg	cfg;
 
 	/* The value last read from the hardware. Used to detect overflow. */
@@ -369,6 +373,7 @@ int mpam_apply_config(struct mpam_component *comp, u16 partid,
 
 int mpam_msmon_read(struct mpam_component *comp, struct mon_cfg *ctx,
 		    enum mpam_device_features, u64 *val);
+void mpam_msmon_reset_mbwu(struct mpam_component *comp, struct mon_cfg *ctx);
 
 int mpam_get_cpumask_from_cache_id(unsigned long cache_id, u32 cache_level,
 				   cpumask_t *affinity);
-- 
2.39.5